Custom number formats in Google Sheets: Issue displaying negative numbers

Context: Looking to display large numbers used in financial reporting & analysis in an abbreviated easier-to-read format.

I currently have the GS custom number format as follows:

[>=999950]#,##0.0,,;[<=-999950](#,##0.0),,;"–"

Which renders positive numbers as desired, e.g. 2338300000 displays as 2,338.3. However, negative numbers aren't working & display as follows:

If I remove the parentheses the negative numbers display in the abbreviated format.

I've looked at the documentation for the GS API https://developers.google.com/sheets/api/guides/formats#meta_instructions but it doesn't seem to have the syntax rules that explain this behavior (or maybe I'm just reading it wrong).